1. Field of the Invention
The present invention relates to ceric oxides exhibiting novel morphological characteristics, and to a process for the preparation thereof.
In the following description of the invention, the term "a specific surface" refers to the B.E.T. specific surface as determined by the BRUNAUER-EMMETT-TELLER method described in the Journal of the American Chemical Society, 1938, 60, 309.
2. Description of the Prior Art
Ceric oxide, by itself or in a mixture of other metal oxides, has been used as a catalyst, and in particular for the synthesis of methanol [C. R. Seances Acad. Sci, Ser. 2. 292 (12) 883-5 (1981)] and in processes for the treatment of residual gases [Japanese Application No. 76/62 616].
To realize good catalytic reactivity, it is generally desirable to utilize a ceric oxide having the largest possible specific surface.
French Patent No. 2,559,754 describes the preparation of a ceric oxide having a specific surface of at least 85.+-.5 m.sup.2 /g, which is obtained after calcination between 350.degree. and 450.degree. C. Preferably, the specific surface is between 100 and 130 m.sup.2 /g after calcination at a temperature in the range from 400.degree. to 450.degree. C.
The method of preparation comprises the hydrolysis of an aqueous solution of ceric nitrate in a nitric acid medium, followed by the separation of the precipitate obtained, washing by means of an organic solvent, optional drying, and calcination between 300.degree. and 600.degree. C. The ceric oxide obtained exhibits a large specific surface but low porosity. The micropores have a median diameter between 10 and 20 .ANG. and a pore volume on the order of 0.02 cm.sup.3 /g.
French Patent No. 2,559,755 describes a method of preparing a ceric oxide having a specific surface of at least 85.+-.5 m.sup.2 /g after calcination between 350.degree. and 500.degree. C., and more specifically, a specific surface of between 150 and 180 m.sup.2 /g after calcination between 400.degree. and 450.degree. C. The method of preparation consists of precipitating a basic ceric sulfate by reacting an aqueous solution of ceric nitrate and an aqueous solution containing sulfate ions, separating the precipitate obtained, washing it with an ammonia solution, optionally drying it, and then calcining it at a temperature between 300.degree. and 500.degree. C. The ceric oxide prepared in this manner has a large specific surface and a wide size range in pores, with the pores ranging from 10 to 200 .ANG., and a pore volume of approximately 0.15 cm.sup.3 /g. The product further contains a quantity of residual sulfate ions, wherefore it may be used only selectively in the field of catalysis.